The present invention relates generally to optical disk recording apparatus for recording desired information onto an optical disk having wobbled recording tracks, and more particularly to an improved optical disk recording apparatus which permits high-accuracy wobble extraction, pre-pit detection, etc. during recording.
Recordable optical disks, such as recordable CDs like CD-R and CD-RW disks and recordable DVDs like DVD-R, DVD+RW, DVD-RAM and DVD-RW disks, have recording tracks wobbled in predetermined cycles. Generally, during recording, a wobble signal is extracted out of a push-pull signal generated by receiving a reflection of a recording laser light beam off the optical disk; specifically, the push-pull signal is indicative of a difference between outputs from light-receiving elements positioned symmetrically about the longitudinal direction of the recording track. Spindle motor control, reproduction of address information, generation of reference clock pulses for a recording signal, etc. are performed on the basis of the extracted wobble signal. Where the optical disk has pre-pits, i.e. marks previously formed intermittently along the recording track in a laterally displaced relation to the centerline of the track, a pre-pit signal (i.e., signal indicative of detected pre-pits) is extracted out of the push-pull signal, and generation of reference clock pulses for a recording signal, reproduction of address information, spindle motor control, etc. are performed on the basis of the extracted pre-pit signal.
During recording, the push-pull signal tends to vary significantly in level under the influence of modulation of the recording laser light beam with the recording signal. The wobble signal can normally be extracted by filtering the push-pull signal, but where the wobble signal and push-pull signal are of frequency bands considerably close to each other, a recording signal component can not be fully separated from the wobble signal by the filtering, so that the recording signal component would remain in the extracted wobble signal as a noise component, which would adversely influence the spindle motor control and the like. Further, the pre-pit signal occurs as a pulse-like projecting signal in the push-pull signal, and thus the pre-pits can be detected by comparing a changing level of the pre-pit signal with an appropriate threshold value. However, because the push-pull signal tends to vary in level under the influence of the modulation of the recording laser light beam with the recording signal, the peak level of the pre-pit signal would also vary. This makes it difficult to set the appropriate threshold value, which would result in erroneous detection of a pre-pit or result in a pre-pit being entirely omitted from detection.